Helices triple

Fibrous proteins can serve as structural materials for the same reason that other polymers do they are long-chain molecules. By cross-linking, interleaving and intertwining the proper combination of individual long-chain molecules, bulk properties are obtained that can serve many different functions. Fibrous proteins are usually divided in three different groups dependent on the secondary structure of the individual molecules coiled-coil a helices present in keratin and myosin, the triple helix in collagen, and P sheets in amyloid fibers and silks. 

FIGURE 6.18 Poly(Gly-Pro-Pro), a collagen-like right-handed triple helix composed of three left-handed helical chains. (Adaptedfrom Miller Scheraga, H. A., 1976, Calculation of the... 

Regulation of mRNA transcription and DNA bending by using triple helix forming oligonucleotide 99YGK194. 

Exopolysaccharides in solution have an ordered helical conformation, which may be single, double or triple for example, xanthan forms a double or triple helix (Figure 7.3c). These are stabilised by intermolecular hydrogen bonds. The helical conformation makes the exopolysaccharide semirigid and the molecules can move large volumes of solution. These volumes overlap even at low concentrations of exopolysaccharide, giving rise to relatively high viscosities. 

Kinetic Aspects of Triple-Helix Formation of Peptide Models Compared with... 

Thermodynamic Aspects of the Triple Helix-Coil Transition. . 186... 

Fig. 1. Schematic representation of the chain alignment of a triple helix. Circles represent o-carbons, that of glycine is denoted number 1. Heavy circles indicate the chain in front, the N-terminal is at the bottom. The intrachain hydrogen bonds are designated by broken lines...

Since these investigations could be carried out only in the crystalline state, the question of the dynamics of the triple-helix formation and of the correlation of its stability with the amino acid sequence could be answered only with the help of other methods working in solution. 

This experiment shows that folding of the non-helix or poor helix-forming sequence is encouraged in the triple helix too, even if this part of the helix contributes to a decrease of the folding strength. Sedimentation and hydrodynamic measurements clearly show the formation of a trimer aggregation and of an extended shape. 

Roth and Heppenheimer371 found that the non-helix forming sequence (Gly-Pro-Leu) inserted between two blocks of (Gly-Pro-Pro) 5 is folded to a triple helix in methanol/water (volume ratio 9 1) (Gly-Pro-Leu)n alone does not fold (Fig. 19). 

It is well known that native collagen containes tripeptide sequences, which alone are not capable of building up a triple helix (e.g. Gly-Pro-Leu, Gly-Pro-Ser) when they exist as homopolypeptides. The synthesis of threefold covalently bridged peptide chains opens up the possibility of investigating the folding properties of such weak helix formers, because the bridging reduces the entropy loss during triple-helix formation and thereby increases the thermodynamic stability of the tertiary structure. Therefore, we have... 

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